1. Field of the Invention
The present invention relates to networking and, more specifically, to a method and system for reliably transmitting IPmc streams of data over a network.
2. Description of the Background Art
While the concept of anycasting is well known, it is most often applied to services where unicast traffic is sent towards an anycast address as a form of redundancy for a service. When IP (Internet Protocol) multicast is used, it is also feasible to source IP multicast traffic from an anycast address to provide server redundancy. Current implementations have some limitations. For example, assume that two or more servers at separate physical locations in a network source the same content. Both servers are assigned the same IP address. A local router for each of the servers is configured to advertise this address to the network as a host route so that clients in the network will connect to the nearest anycast server. One use of anycast servers is to source video data. Anycast multicast video servers in video networks provide both load balancing and redundancy. For example, some video servers receive multiple MPEG ASI video streams that are packetized into separate multicast streams. The servers then send the data as multicast to a destination by way of network routers.
Sometimes, a server will not transmit one or more of its data streams due to loss of input signal to the server. In conventional systems, if only a single data stream from a server goes down (e.g., an MPEG video stream) while all other streams from the server remain up, there is no way to restore the lost single stream, short of manually switching to another server that has all streams up. In this situation, the physical connection between the anycast server and the router has not gone down. The router is sending some legitimate streams of data; it is just not sending all of its streams. Conventional systems determine that a server is unavailable and not sending by looking at the physical interface between the server and the router. Unfortunately, because the physical interface between the anycast server and the router has not gone down, the router will not be able to detect a loss of physical connection and withdraw the host route from the network.
Sometimes a physical connection between a server and a router goes down. If the router connects to the server through switch interfaces, the router will be unaware that the physical link from the server to the switch has gone down. The actual application on the server appliance generating one or more video streams may be incapable of generating a link up/down signaling on its interface.
What is needed is some way for the routers to determine when some but not all streams from a server have gone down so that the router can withdraw the associated anycast host route from the network and force the network to switch to a remaining anycast source in the network.